Miley Cyrus -- Intruder Sentenced to Year-and-a-Half in Jail

The scissor-wielding man who snuck onto Miley Cyrus' property last month has just been sentenced to 18 months in jail for trespassing and resisting arrest ... TMZ has learned.

The L.A. City Attorney tells TMZ, Jason Luis Rivera refused probation for some unknown reason, meaning Rivera received a cut-and-dry jail sentence with no strings attached.

FYI -- 18 months is the MAXIMUM sentence for his crimes.

Rivera is currently in custody and will begin serving his sentence immediately. The temporary restraining order -- blocking Rivera from going near Miley and her home -- was NOT extended as part of the sentencing.